In a typical battery powered portable wireless communications device, such as a cellular telephone or a personal communicator, referred to herein as a mobile station, the receiver baseband filter and analog to digital converter (ADC) are large consumers of current. In a typical case the operational characteristics of these components, such as filter order for the base band filter and the dynamic range of the ADC, are established according to some assumed worst case reception conditions. In practice, however, these worst case reception conditions are rarely encountered. As a result, the baseband filter and ADC are typically operated in a higher current consumption mode than is required for the actual reception conditions.
One problem that results from the excessive power consumption is a reduced standby time for the mobile station, which results in turn in a requirement to more frequently recharge the battery. One type of wireless system where this problem may exist is based on Wideband Code Division Multiple Access (WCDMA), although other types of mobile stations, such as those based on Time Division Multiple Access (e.g., GSM-compatible mobile stations) can also be affected.
FIG. 5 shows a typical WCDMA network situation, where a population of mobile stations (MSs) 1 are contained within a macrocell 3 served by a macro base station (BS) 2, and where some of the mobile stations 1 may also be located within a picocell or a microcell 5 served by a pico/micro base station 4. For comparison, and by example, the macrocell 3 may have a diameter measured in tens of kilometers, the microcell may have a diameter that is a kilometer or less (e.g., it may cover an airport or a shopping mall), while the picocell may have a diameter measured in some tens of meters (e.g., within an office). Although physically located within the microcell 5, some of the MSs, such as the one designated MS_A, may actually be served by the macrocell BS 2.
An adjacent channel test is currently used to measure the capability of the MS to tolerate a signal having a frequency located adjacent to a desired carrier frequency. In the current WCDMA system an Adjacent Channel Selectivity (ACS) parameter is defined to be 33 dB, meaning that the MS receiver must be capable of providing up to 33 dB of attenuation to an adjacent frequency channel. In practice, however, the 33 dB of attenuation is not typically required. For example, in FIG. 5 the MS designated MS_A is connected to the macrocell BS 2 through a first frequency channel and is at the same time physically close to the microcell BS 4, that happens to be operating in a second frequency channel that is adjacent in frequency to the first frequency channel. The signal of the microcell BS 4 is thus received by the MS_A with significant power, and the entire 33 dB of ACS attenuation may be required for the MS_A to continue operating with the macrocell BS 2, while the remainder of the population of MSs 1 served by BS 3, i.e., those not physically near to the microcell BS 4, the 33 dB of ACS attenuation is not required. However, if the MSs are designed to always exhibit the maximum ACS attenuation of 33 dB, the result is unnecessary power consumption.
What is thus needed, and what was not available prior to this invention, is a technique for the MS to determine whether the full amount of ACS attenuation is required, or whether less attenuation is adequate in light of the current reception conditions.